After graduating from Harvard, Gregg sailed to India on January 1, 1925 to learn about Indian culture and to seek out Gandhi.[7] His publications include Gandhiji's Satyagraha or non-violent resistance, published in 1930, and The Power of Non-Violence, from 1934. His revision, The Power of Non-Violence (1960) included a foreword by King. The book was republished in several other editions, including a Swedish translation in 1936 (as Den nya maktfaktorn: motstånd utan våld). Gregg's 1939 pamphlet Pacifist Program in time of war: threatened war, or fascism was a program detailing how American pacifists could use non-violence to oppose war and fascism in the United States.[8] In the 1940s Gregg became interested in ecology and organic farming, and spent several years living on a farm owned by Scott and Helen Nearing. [9] Gregg was also author of other books, including The Compass of Civilization, and the essay The Value of Voluntary Simplicity (Wallingford, PA: Pendle Hill, 1936), a philosophical essay on the need and benefits of living more simply. He coined the term "voluntary simplicity". "A Preparation for Science" ( Gujarat Vidyapith,1928 )- This book was mainly intended for preparing primary school teachers in rural India who can teach science to the rural children using locally available materials. He had envisioned that science education is an absolute must for the Indian children.

^Huxley, Aldous and Baker Robert S.(ed.) (2002). Complete Essays, 1936-1938. Volume 4. I.R. Dee. pp. 240, 248. See also the reference to Gregg's The Power of Non-Violence in Huxley's Ends and Means (1937).